Security surge at Boston Marathon

THOUSANDS OF uniformed and undercover police officers will blanket the Boston Marathon Monday, three years after three spectators were killed in a terrorist attack at the finish line.

Security measures include stepped-up patrols, explosives-sniffing dogs, more surveillance cameras, a no-fly zone over the route and helicopter sweeps to detect any use of a radiological “dirty bomb.”

Spectators are asked to leave backpacks and other large bags at home and carry only clear, easily searchable plastic bags.

More than 260 others were injured when a pair of terrorist brothers set off pressure-cooker bombs near the finish line of the nation’s oldest marathon.

Older brother Tamerlan Tsarnaev was killed in a suburban shootout with authorities. Dzhokhar Tsarnaev was apprehended after an intense manhunt where officials asked residents in and around Boston to stay indoors.

Sunday afternoon, with the race just hours away, runners, supporters and tourists enjoyed a festive atmosphere.

Pots of yellow daffodils lined the sidewalk outside the Marathon Sports athletic store — the site of one of the two bombs that exploded near the finish line on April 15, 2013.

The marathon, which began April 19, 1897, is expected to draw more than 30,000 runners from 99 countries — the third-largest field in the history of the race — and 1 million onlookers.

There’s a total of $830,500 in prize money up for grabs.